Values shown in Table 1 illustrate the nutrient content in different manure storage systems but do not represent the full range of variation within a species or among manure storage syst
Trang 1Nutrient Management: Diet Modification
Terry J Klopfenstein
University of Nebraska, Lincoln, Nebraska, U.S.A
INTRODUCTION
Animal feeding operations are becoming more
concen-trated and the U.S EPA (Environmental Protection
Agency) has proposed more restrictive requirements
Great progress has been made in diet modifications
designed to reduce animal excretion of nutrients The
nutrients of primary concern are nitrogen and phosphorus
PHOSPHORUS UTILIZATION
Phosphorus (P) is an essential mineral nutrient required
for bone growth and maintenance and for most body
metabolic functions such as energy utilization
Phospho-rus has been supplemented to animal diets in mineral form
such as dicalcium phosphate produced from mined
mineral deposits Typically, phosphorus was fed above
the requirement of the animals as a safety factor due to lack
of confidence in the precise P requirements and supplies P
in manure can build up in soils and subsequently
con-taminate ground water if not properly managed P
require-ments are quite different for ruminants (cattle and sheep)
and nonruminants (pigs and chickens), and P is
metabo-lized differently by ruminants
Poultry and swine grow rapidly and therefore require
high levels of P in their diets (up to 6% of diet;[1–3])
Much of the P in feed ingredients (such as corn and
soybean meal) is in the form of phytate P Swine and
poultry lack the enzyme (phytase) necessary to utilize the
phytate P so it appears in the manure Inorganic P must be
supplemented to meet the animal’s requirements This
makes P use very inefficient (10 to 20%) and most of the P
ends up in the manure There are four technologies that
producers can use to reduce P excretion
1 Feeding to requirements Ongoing research is helping
to more precisely define P requirements for each
type of production and for animal ages within each
type of production With modern technology, it is
possible to formulate diets quite precisely so that P is
not overfed.[1]
2 Phytase This enzyme is produced commercially
through microbial fermentations and can be added to
swine or poultry diets Phytase releases the organic P from phytate and makes it available to the animal.[4,5] Therefore, the phytate P in corn and soybeans, the primary feedstuffs in swine and poultry diets, is utilized to meet the animal’s requirements, reducing the need for supplement
3 Phase feeding Swine and poultry grow rapidly Bone growth is very rapid in young animals and is essentially zero in mature animals Therefore, the requirement for P decreases as the animals grow and mature.[2,3] Phase feeding is the process of changing diets to reduce the amount of P In the past, two or three diets may have been fed, but now the number is increasing to five or six Phase feeding, combined with precise formulation and precise requirements, decrease dietary P and therefore manure P.[1]
4 Low phytate feeds Genetically enhanced low-phytate corn and soybean meal are available The total P in these feedstuffs is not necessarily lower, but the P is in the available, inorganic form rather than the organic (phytate) form.[1,6] Feeding low-phytate corn and soybeans can decrease P excretion by 50%
Beef and dairy cattle digest and metabolize P somewhat differently than nonruminants The microorganisms in the rumen digest the P in phytate, making the P available to the animal Beef and dairy cattle tend to grow slower and have lower P requirements than nonruminants.[7,8] Lac-tating dairy cows excrete considerable amounts of P in milk so cows giving milk have higher requirements higher requirements for higher producers.[8]
The most important issue with ruminants is to establish precise requirements and then formulate diets to meet but not exceed requirements The requirements for lactating dairy cows is about 30% of the diet.[9] The ingredients (corn, supplemental protein, silage, alfalfa) fed to dairy cows will supply most, if not all, of this requirement Beef cattle in feedlots are typically fed diets high in corn grain, which contains 25 to 3% P Recent research suggests the requirement for feedlot cattle is 12 to 14%.[10]The problem is that the ingredients in the feedlot diets (primarily corn) have nearly 3% P There does not seem to be any practical way of reducing dietary P levels below 25% and therefore, P excretion by feedlot cattle is relatively high
DOI: 10.1081/E EAS 120019731 Copyright D 2005 by Marcel Dekker, Inc All rights reserved.
Trang 2NITROGEN UTILIZATION
Nitrogen (N) is a part of amino acids (AA) that form
proteins required by all animals; animals consume protein
and AA and then excrete various forms of N If N in
manure is not managed appropriately, it can contaminate
surface and ground waters (nitrate) Just as important is
the volatilization of N (NH3) from manure The resulting
NH3(ammonia) adds to odors and can be redeposited on
cropland or environmentally sensitive areas such as lakes
and streams
Swine and poultry must be fed essential AAs to meet
requirements Because of rapid lean growth, AA
require-ments are high and must be met to produce optimal body
weight gains and feed efficiencies.[2,3] However, if any
AA is fed above the requirement, that AA will be used for
energy and the N excreted
IDEAL PROTEIN
The ideal protein is a protein with a balance of amino
acids that exactly meets an animal’s AA requirements.[11]
By formulating diets to ideal protein content, no excess
AAs are fed and N excretion is minimized Formulation
for ideal protein can be accomplished by using
high-quality protein sources with good balances of AA and
protein sources that complement the AA balance in corn
The greatest opportunity is to use crystalline AA to
bal-ance for AA deficiencies Lowering the dietary protein
content by two percentage points and supplementing with
crystalline AA results in a 20 to 25% decrease in N
ex-cretion in swine or 30 to 40% in poultry.[12]
FEED ADDITIVES
Feed additives or feeding management systems that
in-crease feed efficiencies also inin-crease efficiency of N
uti-lization Ractopamine increases lean growth in swine and,
therefore, increases N-use efficiency.[1]
PHASE FEEDING
Amino acid requirements decrease as swine and
poul-try grow, just as the P requirement decreases Balancing
diets to ideal protein and changing diets often as pigs or
poultry grow decrease the protein fed and, therefore, the
N excreted.[1]
NITROGEN FOR RUMINANTS Cattle are unique because of the microflora in the rumen This ability allows them to digest fiber, but does raise some challenges in protein nutrition Protein that reaches the small intestine is a combination of microbial protein and undegraded feed protein This protein (metabolizable protein, MP) is digested and absorbed in a manner similar
to nonruminants The growing beef animal and lactating dairy cows have two requirements that nutritionists must meet degradable protein for the rumen microbes and undegraded protein that supplies the additional MP needed by the animal.[7,8] Only recently have these requirements been elucidated, and further refinement of requirements is needed
The greatest opportunity for decreasing N excretion by cattle is to use the MP system to meet but not exceed requirements for degradable and undegradable protein Phase feeding feedlot cattle and group feeding dairy cows have the potential to markedly reduce N excretion Ammonia losses have been reduced by as much as 32%
by using these technologies.[13]There is some reluctance
by nutritionists to reduce levels of degradable and undegradable protein because of concern that milk or beef production will be compromised Research indicates that will not happen, but it is more difficult to control variables in commercial production facilities.[14–16]
CONCLUSION Phosphorus and nitrogen excretion can be reduced markedly by the use of new technologies In the future, there will be incentives for producers and nutritionists to make use of these technologies
REFERENCES
1 Klopfenstein, T.J.; Angel, R.; Cromwell, G.L.; Erickson, G.E.; Fox, D.G.; Parsons, C.; Satter, L.D.; Sutton, A.L Animal Diet Modifications to Decrease the Potential for Nitrogen and Phosphorus Pollution; Council for Agricul tural Science and Technology: Ames, IA, 2002 CAST Issue Paper Number 21
2 National Research Council Nutrient Requirements of Poultry, 9th Ed.; National Academy Press: Washington,
DC, 1994
3 National Research Council Nutrient Requirements of Swine, 10th Ed.; National Academy Press: Washington,
DC, 1998
4 Kornegay, E.T.; Denbrow, D.M.; Yi, Z.; Ravindran, V Response of broilers to graded levels of microbial phytase
Nutrient Management: Diet Modification 665
Trang 3added to maize soybean meal based diets containing three
levels of non phytate phosphorus Br J Nutr 1996, 75,
839 852
5 Cromwell, G.L.; Stahly, T.S.; Coffey, R.D.; Monegue,
H.J.; Randolph, J.H Efficacy of phytase in improving the
bioavailability of phosphorus in soybean meal and corn
soybean meal diets for pigs J Anim Sci 1993, 71, 1831
1840
6 Cromwell, G.L.; Traylor, S.L.; White, L.A.; Xavier, E.G.;
Lindemann, M.D.; Sauber, T.E.; Rice, D.W Effects of
low phytate corn and low oligosaccharide, low phytate
soybean meal in diets on performance, bone traits, and
P excretion by growing pigs J Anim Sci 2000, 78
(Suppl 2), 72 (abstract)
7 National Research Council Nutrient Requirements of Beef
Cattle, 7th Ed.; National Academy Press: Washington, DC,
1996
8 National Research Council Nutrient Requirements of
Dairy Cattle, 7th Ed.; National Academy Press: Wash
ington, DC, 2001
9 Wu, Z.; Satter, L.D.; Blohowiak, A.J.; Stauffacher, R.H.;
Wilson, J.H Milk production, estimated phosphorus
excretion and bone characteristics of dairy cows fed
different amounts of phosphorus for two or three years
J Dairy Sci 2001, 84, 1738 1748
10 Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T.; Brink, D.;
Orth, M.W.; Whittet, K.M Phosphorus requirement of
finishing feedlot calves J Anim Sci 2002, 80, 1690
1695
11 Baker, D.H.; Han, Y Ideal amino acid profile for chicks during the first three weeks posthatching Poult Sci 1994,
73, 1441 1447
12 Allee, G.; Liu, H.; Spencer, J.D.; Touchette, K.J.; Frank, J.W Effect of Reducing Dietary Protein Level and Adding Amino Acids on Performance and Nitrogen Excretion of Early Finishing Barrows In Proceeding of the American Association of Swine Veterinarians; Amer ican Association of Swine Veterinarians: Perry, PA, 2001;
527 533
13 Erickson, G.E.; Klopfenstein, T.J.; Milton, C.T Dietary Protein Effects on Nitrogen Excretion and Volatilization in Open dirt Feedlots In Proceedings of the Eighth Interna tional Symposium on Animals, Agriculture and Food Processing Wastes; ASAE Press: St Joseph, MO, 2000;
204 297
14 Satter, L.D.; Klopfenstein, T.J.; Erickson, G.E The role of nutrition in reducing nutrient output from ruminants
J Anim Sci 2002, 80 (E Suppl 2), E143 E156
15 Klopfenstein, T.J.; Erickson, G.E Effects of manipulating protein and phosphorus nutrition of feedlot cattle on nutrient management and the environment J Anim Sci
2002, 80 (E Suppl 2), E106 E114
16 Wang, S.J.; Fox, D.G.; Cherney, D.J.; Chase, L.E.; Tedeschi, L.O Whole herd optimization with the Cornell net carbohydrate and protein system III Application of
an optimization model to evaluate alternatives to reduce nitrogen and phosphorus mass balance J Dairy Sci 2000,
83, 2160 2169
666 Nutrient Management: Diet Modification
Trang 4Nutrient Management: Water Quality/Use
J L Hatfield
United States Department of Agriculture, Agricultural Research Service, Ames, Iowa, U.S.A
INTRODUCTION
Animals generate a valuable source of nutrients in both
organic and inorganic forms Nutrients in manure can be a
valuable soil amendment; however, if manure is misused,
it can be a potential water quality problem Water quality
is a primary concern among environmental issues; manure
application is the focus of this article
MANURE NUTRIENTS
Nutrients vary among species, manure handling, and
storage systems as shown in Table 1 Nutrient content is
affected by species, diet, age, sex, manure storage system,
and length of time in storage Values shown in Table 1
illustrate the nutrient content in different manure storage
systems but do not represent the full range of variation
within a species or among manure storage systems
These data provide an indication of the variation
among species and the need for nutrient management
systems to consider animal production systems and
manure storage systems before making assumptions about
the best management system The goal in nutrient
management is to develop a system in which manure
nutrients may be applied to the soil to supply the crop
needs without being a potential environmental problem
WATER QUALITY CONCERNS
In nutrient management, water quality concerns focus on
phosphorus (P) and nitrate-nitrogen (NO3-N) Broadcast
manure on the soil surface provides for potential surface
runoff conditions, particularly when rain occurs shortly
after application In a 2001 study, broadcasting manure
resulted in the greatest potential for surface runoff of
soluble P.[2] Kleinman and Sharpley[3] compared
dis-solved reactive phosphorus from three manures at six rates
under simulated rainfall and found that dissolved reactive
phosphorus loss was related to runoff and manure
application rate Soluble P losses were a function of the
type of manure, the application rate, and soil type
Broadcast manure on the soil surface increases the
potential for surface runoff into nearby surface water
bodies In addition, surface runoff of manure may provide pathogens that are present in manure a pathway into nearby water bodies There are few studies of this problem and the evidence is insufficient to provide a set of factors that contribute to pathogen movement
Incorporation of manure into the soil greatly reduces the chances of surface runoff Tabbara[4] showed that incorporation of manure or fertilizer 24 hours before a heavy rainfall reduced both dissolved reactive P or total P concentrations by as much as 30% to 60% depending on the nutrient source and application rate The incorporation process moves P below the volume of soil eroded under high rainfall events To reduce potential surface losses of
P, manure should be incorporated on soils with intensive erosive rain, recent extensive tillage, or little or no surface residue Incorporation of manure will reduce the likeli-hood of surface runoff of P and protect surface water from excess P levels; however, the process of incorporating manure may increase the potential for sediment loss from the soil The development of management practices that protect soil from surface runoff will decrease potential losses of manure P into nearby water bodies
Incorporation of manure may lead to NO3-N leaching because nutrients placed below the surface mixing layer are in a soil volume where leaching of nutrients can occur
NO3-N present in the manure may be moved into deeper soil layers by soil water However, there is no evidence that this is a direct result of manure application Incorporation of manure changes the availability of nutrients in the soil profile Nutrients present in manure are in the organic form and the conversion into available forms is a function of biological activity and time in the soil profile Klausner et al.[5] developed a method to estimate the decay rate for organic nutrients from dairy manure that has worked well for this species over a range
of environmental conditions One of the challenges for manure management is to determine the temporal patterns
of nutrient availability from different manure types and species Jokela[6]showed that NO3-N levels were actually lower in soils treated with dairy manure compared to commercial fertilizer because of the slower release of
NO3-N from manure
Nutrient patterns in manured soils can lead to potential water quality problems; however, these can be managed through a proper rate of application and incorporation
DOI: 10.1081/E EAS 120019732
Published 2005 by Marcel Dekker, Inc All rights reserved.
Trang 5Water quality problems can be reduced through relatively
simple management practices that increase nutrient
availability to the crop and decrease the potential for
offsite movement through runoff or leaching
EFFECT OF MANURE ON SOIL PROPERTIES
RELATED TO WATER QUALITY
Addition of manure to soil causes changes in the soil
properties[7,8]that reduces the likelihood of water quality
problems Water infiltration rate, soil water-holding
capacity, cation exchange capacity, bulk density, organic
matter, biological activity, and plant availability of
nutrients are changed by manure additions These changes
required at least five years of manure additions to the
soil A positive impact on water quality is derived from
increased water infiltration rates and water storage
ca-pacity Surface runoff occurs in soils that quickly develop
a surface seal and ponding begins on the soil surface leading to the development of small rills that transport water along the surface Manure-amended soils have a larger infiltration rate and more rainfall can enter the soil before saturation occurs This change is not a direct ef-fect of manure addition but a combination of increased biological activity and organic materials that create a more stable soil particle that has a higher soil water content before becoming saturated The higher water-holding capacity of soil allows more absorption before the profile is saturated Eghball et al.[9] concluded that the increased intensity of rainfall could cause surface runoff but changes in the soil properties from manure could offset water quality problems
Addition of manure to soil not only changes the soil properties but also restores the soil to a higher level of soil productivity Freeze et al.[10] found that the applica-tion of manure to eroded soil was of greater benefit than application to noneroded soils Changes in soil
Table 1 Nutrient content in solid and liquid manure for different species and manure handling systems
Species
Dry matter %
Dry matter %
(From Ref 1.)
Fig 1 Conceptual diagram of nutrient flows in the MINAS systems for the Netherlands (Adapted from Ref 11.)
668 Nutrient Management: Water Quality/Use
Trang 6properties are more detectable in eroded soils These
effects of manure can be realized with all sources and
types of manure Often the water quality problems that
occur in agriculture are from soils that are in a
degrad-ed state and restoration of soil properties will benefit
the environment
NUTRIENT ACCOUNTING FROM
MANURE SOURCES
To achieve water quality goals and manure application
requires the proper amount of nutrients added to the soil to
supply crop requirements The components in a nutrient
budget are rates of crop removal, change in the soil
nutrient content, and amount supplied from manure In the
Netherlands, nutrient accounting systems have been
developed for livestock and cropping systems Ondersteijn
et al.[11] described the mineral accounting system
(MINAS) and provided a framework for nutrient
account-ing (Fig 1) Manure that is produced is accounted for
through the MINAS approach to ensure that both an
economic and environmental quality goal is achieved
Development of nutrient management guidelines for
producers to help guide their decisions can have a positive
impact on environmental quality
CONCLUSION
Nutrient management programs must have a positive
impact on water quality The challenge for producers is to
understand the nutrient balance in the soil and to reduce
the risk of surface runoff of manure The challenge for
science is to increase our understanding of the value of
manure in the soil and in the restoration of eroded soils to
a higher level of productivity Improved methods for
sampling manure to determine the nutrient content from
individual farms and for manure application that
incor-porates manure to reduce erosion and enhance the value of
manure on soil properties will benefit livestock, crop producers, and the environment
REFERENCES
1 MWPS (MidWest Plan Service) Manure Storages Ma nure Management System Series MWPS 18, Section 2 MidWest Plan Service Iowa State University: Ames, IA,
50011 3080, 2001
2 Zhao, S.L.; Gupta, S.C.; Huggins, D.R.; Moncrief, J.F Tillage and nutrient source effects on surface and subsurface water quality at corn planting J Environ Qual
2001, 30, 998 1008
3 Kleinman, P.J.A.; Sharpley, A.N Effect of broadcast manure on runoff phosphorus concentrations over succes sive rainfall events J Environ Qual 2003, 32, 1072 1081
4 Tabbara, H Phosphorus loss to runoff water twenty four hours after application of liquid swine manure or fertilizer
J Environ Qual 2003, 32, 1044 1052
5 Klausner, S.D.; Kanneganti, V.R.; Bouldin, D.R An approach for estimating a decay series for organic nitrogen
in animal manure Agron J 1994, 86, 897 903
6 Jokela, W.E Nitrogen fertilizer and dairy manure effects
on corn yield and soil nitrate Soil Sci Soc Am J 1992,
56, 148 154
7 Sommerfeldt, T.G.; Chang, C Changes in soil properties under annual applications of feedlot manure and different tillage practices Soil Sci Soc Am J 1985, 49, 983 987
8 Sommerfeldt, T.G.; Chang, C Soil water properties as affected by twelve annual applications of cattle feedlot manure Soil Sci Soc Am J 1987, 51, 7 9
9 Eghball, B.; Gilley, J.E.; Baltensperger, D.D.; Blumenthal, J.M Long term manure and fertilizer application effects on phosphorus and nitrogen in runoff Trans ASAE 2002, 45,
687 694
10 Freeze, B.S.; Webber, C.; Lindwall, C.W.; Dormaar, J.F Risk simulation of the economics of manure application to restore eroded wheat cropland Can J Soil Sci 1993, 87,
267 274
11 Ondersteijn, C.J.M.; Beldman, A.C.G.; Daatselaar, C.H.G.; Giesen, G.W.J.; Huirne, R.B.M The Dutch mineral accounting systems and the European nitrate directive: Implications for N and P management and farm perfor mance Agric Ecosyst Environ 2002, 92, 283 296
Nutrient Management: Water Quality/Use 669
Trang 7Nutrient Requirements: Carnivores
Duane E Ullrey
Michigan State University, East Lansing, Michigan, U.S.A
INTRODUCTION
Carnivores, broadly defined, sustain themselves by
feeding on vertebrate or invertebrate animal tissues, a
practice observed in both the animal and plant kingdoms
The Venus flytrap (Dionaea muscipula), one of over 500
carnivorous plant species, lives in humid, acidic bogs in
the Carolinas and, like most plants, acquires energy and
nutrients by photosynthesis and through the roots In this
environment, nitrogen and some mineral elements are in
short supply, and these needs are met by capturing insects
attracted to nectar in a specialized leafy trap, functioning
both as a mouth and stomach Animals, of course, do not
possess roots or the mechanisms of photosynthesis Thus,
energy and nutrient requirements of wild carnivorous
animals are acquired principally by consuming vertebrate
or invertebrate prey.[1,2]
Wilson[3] estimated there are about 4000 species of
extant mammals, 9000 of birds, 6300 of reptiles, 4200 of
amphibians, and 18,000 of fish and lower chordates The
nutrient requirements of these species are presumed to be
qualitatively similar, but quantitative nutrient
require-ments have been defined by the National Academy of
Sciences/National Research Council (NAS/NRC) only for
humans and a few domesticated or captive mammals,
birds, and fish Of the species with NRC-defined
require-ments, the cat, mink, tarsiers, rainbow trout, and salmon
are obligate carnivores The NRC also has defined the
nutrient requirements of the dog and fox, but these species
appear to be facultative carnivores and may consume
considerable vegetable matter
CARNIVOROUS MAMMALS
The immediate ancestors of the domestic cat (Felis catus)
were strictly carnivorous, and its needs have been the most
thoroughly studied of any of the obligate carnivores
Although commercial diets for cats may contain vegetable
matter, the nutrients and the amounts that must be present
reflect a long evolutionary dependence on a strictly
carnivorous diet The cat has a simple digestive system,
presumably because digestibility of natural prey tends to
be high, and there is no need for extended food retention
and microbial fermentation Due to its limited ability to
conserve nitrogen, the cat has a high protein requirement, and it converts only negligible amounts of tryptophan to niacin (neither ability is necessary when consuming whole prey) Requirements for blood glucose are met primarily
by gluconeogenesis rather than from dietary carbohydrate, and the cat has a high requirement for arginine for disposal of nitrogen via the urea cycle It requires taurine and arachidonic acid because of limited tissue synthesis (vertebrate prey provide adequate amounts), and it is unable to convert b-carotene (a plant provitamin) to vitamin A Vitamin D3 needs are met by diet because cutaneous concentrations of 7-dehydrocholesterol (provi-tamin D3) are insufficient to support vitamin D photobio-genesis Nutrient needs of the cat have been reviewed by the NRC,[4]and minimal requirements, adequate intakes, and recommended allowances have been published The NRC-recommended allowances for growth, maintenance, late gestation, and peak lactation are presented in Table 1 The mink (Mustela vison) eats small mammals, fish, frogs, crayfish, insects, worms, and birds in the wild Like the cat, its protein requirements are high 38% of dietary dry matter (DM) from weaning to 13 weeks of age, 22 26% for adult maintenance, 38% for gestation, and 46% for lactation.[5] Whether the mink shares the other unique metabolic features of the cat has not been determined
Tarsiers (Tarsius spp.) eat insects (beetles, ants, locusts, cicadas, cockroaches, mantids, moths) and sometimes small vertebrates in the wild Although the quantitative nutrient requirements of tarsiers have not been specifically defined, estimated adequate nutrient concentrations in dietary DM have been proposed.[6] When kept in captivity, tarsiers are often provided crickets
as a major food item Because crickets and other commercially available insects tend to be deficient in certain nutrients (particularly calcium, vitamin A, and vitamin D),[7]specifically formulated diets are offered to these insects for about 48 hours before feeding them to tarsiers so that the insects plus their gut contents will be nutritionally complete.[8–10]
Other obligate carnivorous mammals include felids such as lions, tigers, leopards, cheetahs, and jaguars Aquatic mammals such as dolphins, seals, sea lions, and walruses also are obligate carnivores, but little is known about their quantitative nutrient requirements
DOI: 10.1081/E EAS 120019733 Copyright D 2005 by Marcel Dekker, Inc All rights reserved.
Trang 8Table 1 Recommended nutrient allowances in dietary dry matter (DM) for domestic cats consuming diets containing 4 kcal of metabolizable energy per g of DM
Eicosapentaenoic and
docosahexaenoic acid, %
a
At least twice as much phenylalanine (or phenylalanine plus tyrosine) is required for maximal black hair color as for growth.
b
Recommended taurine allowances are lowest when diets are unprocessed (0.04% of DM) but are increased by extrusion (0.1% of DM) or canning (0.2%
of DM).
(Adapted from Ref 4, recommended allowances for growth of an 800 g kitten, maintenance or late gestation of a 4 kg adult cat, and lactation of a 4 kg queen with four kittens.)
Trang 9CARNIVOROUS BIRDS
The digestive systems of obligate carnivorous birds (such
as hawks and eagles), like their mammalian counterparts,
do not have compartments adapted for microbial
fermen-tation Relatively indigestible portions of prey, such as fur,
feathers, bones, fins, scales, shells, and exoskeletons, may
be separated from more digestible portions by the beak
prior to food ingestion Sometimes, this separation is
accomplished in the gizzard, followed by egestion of
indigestible matter out of the mouth, as in owls.[11]
Although the NRC[12] has defined the nutrient
require-ments of poultry, these species are principally
herbivo-rous Based on present metabolic evidence and the
composition of vertebrate and invertebrate prey, it seems
likely that nutrient needs of carnivorous birds are similar
to those of carnivorous mammals, with adjustments for
differences in reproductive strategy
CARNIVOROUS REPTILES
AND AMPHIBIANS
The long evolutionary association of snakes, crocodilians,
and some lizard families with subsistence on vertebrate
and invertebrate prey suggests that they are obligate
carnivores They tend to have simple gastrointestinal
systems as compared to herbivorous reptiles, although
there are adaptations related to the periodicity of feeding
and to unique characteristics of certain food items
Tortoises are chiefly herbivorous with a few that are
omnivorous Turtles tend to be omnivorous carnivorous
as juveniles and herbivorous or omnivorous as adults
although a few species are mostly carnivorous throughout
life.[13] Studies that define qualitative or quantitative
needs of reptiles are few, although protein and amino acid
needs of the hatchling green sea turtle (Chelonia mydas;
carnivorous as hatchlings, herbivorous as adults) have
been investigated Some studies suggest that young
red-eared slider turtles (Trachemys scripta elegans) and green
anoles (Anolis carolinensis) do not have an elevated
requirement for arginine (as does the cat), and addition of
taurine to a diet based on plant proteins does not improve
growth of young American alligators (Alligator
missis-sippiensis) Also, American alligators appear to convert
linoleic acid to arachidonic acid to some extent, although
rates may not be optimum for maximum growth.[1]When
a purified diet containing adequate tryptophan but no
niacin was administered weekly by stomach tube to bull
snakes (Pituophis melanoleucus sayi) for 132 days, no
signs of deficiency were seen, suggesting that either a
longer period of depletion is necessary to induce niacin
deficiency or metabolic conversion of tryptophan to niacin
may occur in this species.[14] Thus, if these reptiles are
indeed obligate carnivores, their nutrient needs seem to deviate from those of the cat
Most amphibians appear to be obligate carnivores.[13] Adult frogs and toads consume invertebrates and small vertebrates, although most species are herbivorous as larvae (tadpoles) and have a long, coiled intestine permitting them to digest plant matter At metamorphosis, the intestine is much shortened and the diet becomes strictly carnivorous Tadpoles of a few species are carnivorous and have a much shorter gut than do herbivorous tadpoles Salamanders and newts are carniv-orous both as larvae and as adults, feeding on insects, slugs, snails, and worms Caecilians (limbless, viviparous amphibians) prey on worms, termites, and orthopterans Metabolic features characteristic of carnivory have not been well studied in amphibians
CARNIVOROUS FISH Rainbow trout (Salmo gairdneri) and coho salmon (Oncorhynchus kirsutch) have protein requirements of
40% of dietary DM for maximal growth of juveniles and have an absolute requirement for arginine They also lack the ability to synthesize niacin from tryptophan Gluco-neogenesis is important for provision of blood glucose, and essential fatty acid requirements include linoleic acid and eicosapentaenoic acid and/or docosahexaenoic acid.[15]
CONCLUSIONS Qualitative and quantitative nutrient requirements of obligate carnivores generally appear to reflect evolution-ary adaptations to the composition of ancestral diets
REFERENCES
1 Allen, M.E.; Oftedal, O.T The Nutrition of Carnivorous Reptiles In Captive Management and Conservation of Amphibians and Reptiles, Contributions to Herpetology, Vol 11; Murphy, J.B., Adler, K., Collins, J.T., Eds.; Society for the Study of Amphibians and Reptiles: Ithaca,
NY, 1994; 71 82
2 Allen, M.E.; Oftedal, O.T.; Baer, D.J The Feeding and Nutrition of Carnivores In Wild Mammals in Captivity: Principles and Techniques; Kleiman, D.G., Allen, M.E., Thompson, K.V., Lumpkin, S., Eds.; Univ Chicago Press: Chicago, IL, 1996; 139 147
3 Wilson, E The Diversity of Life; Harvard Univ Press: Cambridge, MA, 1992
4 National Research Council Nutrient Requirements of Dogs
Trang 10and Cats; National Academies Press: Washington, DC,
2004
5 National Research Council Nutrient Requirements of Mink
and Foxes, 2nd Rev.; National Academy Press: Wash
ington, DC, 1982
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